Various types of grasses, as web as grain crops, are grown primarily for seeds, and the value of such seed crops is determined by the purity and germination factor of the harvested seeds. The known methods and apparatus for dehulling seeds, or the like, usually consist of submitting the seeds to some type of mechanical or pneumatic effort to break the hubs and then separate the seeds from the hulls.
One such method to separate seeds from hubs is disclosed in U.S. Pat. No. 4,335,151 to Caubet. Caubet discloses a method of separating seeds from hubs by feeding hulls containing seeds, into a turbulent flow of compressed air in a flow passage of sufficient size to accelerate the hulls containing seeds to a high velocity. The flow of compressed air and hubs containing seeds are than fed into a second passage of much larger cross-sectional area then the first passage. This sudden change of volume greatly expands the air density causing mechanical stresses to be exerted onto the hulls of the seeds thereby cracking the grass seed hubs and allowing the seeds to be separated from the hull.
Mechanical method of dehulling becomes ineffective when the force required to remove the seed from the hub also destroys the seed due to mechanical abrasion and high impact with other seeds and hulls.
U.S. Pat. No. 4,933,072 to Beisel discloses a technique of horizontally projecting a flow mixture of seed, hubs, and hulls containing seeds utilizing pressurized air to propel the flow mixture through a venturi nozzle and coanda curve combination into a classification chamber. That technique proves to be ineffective when the hulls comprise the substantial weight of the hull and seed combination.
U.S. Pat. No. 4,505,196 to Beisel discloses a seed dehuller that has a momentum type separator that is capable of batch dehulling and separating seeds from hulls. That type of separator will periodically expose seeds to high air pressure and then to a period of substantially reduced air pressure to effect the dehulling of the grass seeds. During the period of reduced air pressure the heavier seeds will be separated from the hulls by their greater momentum and directed into a collection bin. That particular type of separator disclosed by Beisel prove ineffective when the grass seed or grains to be dehulled have extremely hard shells such as buffelgrass seed.
Buffelgrass seed is a very hearty and fast growing type of grass. However, buffelgrass seed has a tender seed and a very hard hull that impedes germination of the seed once the seed is planted in the earth. Comparative test results have established that if the hull is removed from buffelgrass seed before planting, an approximate 20-fold increase in germination of the planted seed can be expected.